This invention relates to automated data storage libraries, and, more particularly, to the control of the automated functions of the library for accessing data storage media in response to received commands.
The typical automated data storage library comprises an accessor having a gripper for accessing data storage media, and an XY system having servo motors for moving the accessor in the X direction and the gripper in the Y direction. In some libraries, the X direction is a straight horizontal direction, with storage shelves for the data storage media and the data storage drives arranged in columns and rows on one or both sides of the accessor, and in others, the X direction is a circumferential horizontal direction, with the storage shelves arranged around the outer band of an inner cylinder and storage shelves and drives arranged around the inner band of an outer cylinder, and in both, the Y direction is vertical.
Also typically, the host system, such as a host server, communicates with a central controller for the library, either directly or through one or more data storage drives, providing commands to access particular data storage media and move the media between the storage shelves and the data storage drives, as well as I/O shelves and pass thru slots. The commands may be logical commands identifying the media and/or logical locations for accessing the media. The central controller includes a processor for receiving the logical commands and converting the commands to physical movements of the accessor and gripper. The central controller is typically mounted in the frame, but has been mounted on an accessor, and is connected by direct wiring, or wireless link such as infrared, to the XY system and to the gripper and directly operates the servo motors to conduct the desired physical movements. Of necessity, the wiring required between the central controller and all of the elements of the library becomes highly complex.
It is desirable to allow for expansion in the library to include additional storage shelves and data storage drives. In a straight horizontal library, this may be accomplished by adding expansion frames at one end of a base frame. However, adding expansion frames changes the physical size of the library and the many wiring cables must grow longer. As an example, an IBM 3494 automated data storage library is scaleable up to 16 frames. In order to simplify the part count and to simplify the process of expansion, it may be desirable to therefore provide all base frames for the library with the longest possible wiring cables. Thus, the library may be expanded to the maximum number of frames without requiring complete wiring changes. However, extra storage space must be provided in the base frame to house the extra length of these cables in libraries which are less than maximum length.
In a cylindrical library, or those that are not expandable, no additional frames are provided, and, instead, additional complete libraries must be provided, which are interconnected by pass through slots in which data storage media may be exchanged between the libraries. This results in requiring specialized control structures to track the data storage media in the multiple libraries.
It may also be advantageous to add a second accessor and gripper to an automated data storage library to add redundancy and to speed the access to data storage media. Typically, the second accessor is mounted to move in the X direction from a garage area at the end of the library opposite to the base frame. However, this adds complexity to the central controller and to the cabling, which now must reach from the base frame to the garage at the end of the library opposite the base frame and then back to the maximum distance that the accessor is allowed to travel. Alternatively, a second central controller may be provided at the far end, but many of the control signals and cabling must be shared.
Thus, the wiring necessary for scalability becomes complex and the wiring cable lengths from a central controller may reach undesirable distances and require inefficient space utilization to store the extra cabling for less than maximum length libraries.
As an example of the complexity of the library, the X and Y servo motors are typically DC brushless motors which require many power and signal wires that have to propagate all the way back to the base frame through multiple flex cables and intermediate connections. As the result, signals tend to degrade over the longer wires and multiple connections, there is susceptibility to noise and cross talk, a failure is difficult to isolate and repair, and electrical characteristics may change if the cable lengths are changed.
An object of the present invention is to provide a control system for an automated data storage library which allows the reduction of overly lengthy cabling and allows modular extension to the library and redundancy for the library.
A distributed control system is provided for an automated data storage library. The automated data storage library accesses data storage media in response to received commands, and comprises an accessor having a gripper for accessing the data storage media, and an XY system having servo motors for moving the accessor and moving the gripper. The distributed control system comprises a communication processor node for receiving commands, the communication processor node providing a communication link for the commands. An accessor processor node located at the accessor is coupled to the communication processor node, the accessor processor node responsive to the linked commands, operating the gripper and providing move commands. An XY processor node located at the XY system is coupled to the accessor processor node, the XY processor node responsive to the move commands, operating the XY servo motors.
In one embodiment, the accessor processor node is positioned at the gripper of the accessor.
In another embodiment, a common bus is provided, coupling the communication processor node to the accessor processor node, and coupling the accessor processor node to the XY processor node.
In still another embodiment, an extension frame is provided with an extension common bus coupled to the base frame common bus, and possibly another communication processor node located in the extension frame for receiving commands, the communication processor node coupled to the extension common bus, the communication processor node providing a communication link for the commands to the extension common bus, whereby the commands are linked to the base frame common bus and to the accessor processor node.
In a further embodiment, the automated data storage library may additionally have a high availability frame adjacent an extension frame, or adjacent the base frame. The high availability frame has another accessor having a gripper for accessing the data storage media, and an XY system for moving the accessor and gripper, e.g., in the X and Y directions. The distributed control system additionally comprises an extension common bus coupled either directly to the common bus of the base frame or to the base frame via an extension common bus of an extension frame. Another communication processor node is provided for receiving commands, the communication processor node coupled to the high availability frame extension common bus, the communication processor node providing a communication link for the commands to the extension common bus. An accessor processor node is located at the other accessor, coupled to the high availability frame extension common bus, and is responsive to the linked commands of the communication processor nodes, operating the gripper and operating the servo motors.
For a fuller understanding of the present invention, reference should be made to the following detailed description taken in conjunction with the accompanying drawings.